flesh out README

README.rst

@@ -1,3 +1,25 @@
 freenect2: Python bindings to libfreenect2
 ==========================================
 
+The freenect2 module provides a Python interface to the `libfreenect2
+<https://github.com/OpenKinect/libfreenect2>`_ library.  The libfreenect2
+library provides a library allowing depth and RGB data to be extracted from a
+Kinect for Windows v2 (K4W2) device.
+
+Although a lot of libfreenect2 functionality is exposed, simple "single grab"
+usage of freenect2 should be simple. For example, here is how to grab a single
+depth frame and save it to a grayscale JPEG:
+
+.. code:: python
+
+    from PIL.ImageMath import eval as im_eval
+    from freenect2 import Device, FrameType
+
+    device = Device()
+    with device.running():
+        for frame_type, frame in device:
+            if frame_type is FrameType.Depth:
+                # Convert range of depth image to 0->255.
+                norm_im = im_eval('convert(I / 16, "L")', I=frame.to_image())
+                norm_im.save('depth.jpg')
+                break